Michele Bachmann and Herman Cain are not scheduled to speak, either. They have decided to stage their own mini-convention of sorts — calling it a “unity rally” to dispel any doubts about their party loyalty — at a megachurch about 20 minutes outside town.

Gov. Rick Perry of Texas is trying to be a good sport about getting passed over for a speech. “That’s not my call to make,” he said in an interview this week. “The convention is for Mitt Romney, not for me. Not for Newt, not for Marco Rubio, not for Chris Christie. It’s for Mitt.”

As Mr. Romney and his team make the final adjustments to their plans for the convention, which opens here in two and a half weeks, they are grappling with the delicate questions that hang over these quadrennial gatherings of clashing ambition, competing political agendas and outsize egos. Add to this year’s mix personalities colorful enough to fill a reality show, and the fastidiously controlled, leave-nothing-to-chance Romney campaign has faced some hazardous casting choices. And what they decide could turn off the independent voters their carefully choreographed convention is meant to sway.

Take the two Republicans who literally are reality stars: Donald Trump and Sarah Palin. Though neither has been formally named to speak yet, convention planners are still considering adding both to the schedule. The Romney campaign declined to comment on any speakers that had not been announced yet.

Despite being unpredictable and polarizing, both are popular with certain elements of the party base. In an interview, Mr. Trump happily explained his appeal with voters. “They like what I say,” he said. “I’m a very popular guy, as crazy as it might sound. It’s nice to be loved.”

So loved, in fact, that the high demand for Trump appearances may just conflict with his ability to be in Tampa that week, he said. “The Republican Party in Sarasota — you’ve probably heard of this — they’re giving me the Statesman of the Year award,” he said, adding that he did not want to overextend himself. (As quantitative proof of his popularity, Mr. Trump’s spokeswoman called immediately after the interview to note that he has 1.4 million Twitter followers, a number that she said is growing by about 40,000 a week.)

Inviting Mr. Trump to speak, as risky as that could be, is actually a way for the Romney campaign to exercise some degree of control over what he might say, like his demands that President Obama prove his American citizenship. They would vet and approve whatever remarks he makes — an option they wouldn’t have if they denied him a slot and left him to his own devices on cable television.

But others could prove even more difficult to muzzle. Mr. Cain said that there were still many Tea Party Republicans who felt that Mr. Romney had not heard their concerns.

“What we represent and who we represent deserves a level of respect,” he said, adding that were he to speak, the convention might be a little more interesting.

“Based upon having done hundreds of speeches and based upon the reaction from those various audiences,” he said, “me speaking at the convention could offer, No. 1, some enthusiasm. No. 2, some inspiration to get past any differences that still exist amongst various groups. And let’s be honest, it’s there. We’re not a homogeneous party yet.”

After a primary that was especially divisive and bruising, making everyone at the convention happy was never going to happen. And Mr. Romney is not the first to face such challenges; the campaign of Michael S. Dukakis agonized over the role of Jesse Jackson after Mr. Dukakis beat him for the Democratic nomination in 1988, for example.

But the Romney approach to planning who speaks and who doesn’t — a process that is relentlessly scrutinized for clues about who has fallen in and out of favor with the likely nominee — has prized efficiency and practicality over sentimentality.

With ABC, CBS and NBC expected to provide only an hour of prime-time coverage each night of the convention, planners said the need to keep the program tight and on schedule was a more important consideration than the hurt feelings that might arise from excluding someone.

That means for now, Mrs. Bachmann, Mr. Perry, Mr. Cain and Mr. Gingrich are out. Rick Santorum, the only Republican to challenge Mr. Romney seriously in the delegate count, will speak. Representative Ron Paul will not. But his son Rand, a senator from Kentucky, will. That gesture could help appease Ron Paul agitators who might be looking to disrupt the proceedings, a threat that convention organizers are taking seriously.

But the fissures within the party will not be so easy to paper over, Mr. Gingrich said.

“The tension between the emerging party wings and the traditional party is going to be permanent and will mark the next eight years if Romney is president or if he’s not,” he said. “It’s just a fact.”

Still, Mr. Gingrich insisted that he planned to play nice in Tampa. He is focused on preparing his lesson plans for Newt University, he said, not on sowing any further party discord. “The truth is the hardest-core conservatives didn’t win the nomination. So to turn to Romney and say, ‘You now have to dance to our tune’ doesn’t make much sense to me.”

Mrs. Bachmann angered many fellow Republicans after she demanded an investigation into radical Islamic influence in the United States government, very likely dooming her chances of getting a formal convention role. Nevertheless, she said that not getting behind Mr. Romney would weaken Republicans as they try to unite against their common enemy: President Obama.

“We’ve spoken about this, and we are all together in our conversations,” she said. “You won’t hear any ripple, I don’t think, from any of the candidates who ran in the primaries because we realize what’s at stake.”

But that does not mean the competitiveness is entirely gone. Mr. Perry, for instance, offered that Mr. Romney might benefit from his help on the campaign trail in the fall. He would play the offensive lineman to Mr. Romney’s running back.

“Most running backs know the reason they were successful is that there was a real good interior lineman who was looking for holes,” Mr. Perry said. “I see that as my role.”

A version of this article appears in print on August 9, 2012, on page A14 of the New York edition with the headline: Many Clamor for Convention Roles, but More Are Out Than In. Order Reprints|Today's Paper|Subscribe